1. Field of the Invention
The present invention relates to an integrating A/D converter capable of being applied to a solid-state imaging device typified by a CMOS image sensor, an integrating A/D conversion method, a solid-state imaging device and a camera system.
2. Description of the Related Art
A configuration in which integrating analog/digital converters (hereinafter referred to as A/D converters (Analog Digital converters)) are arranged in parallel in respective columns of an image sensor is proposed (refer to JP-A-2005-323331 (Patent Document 1)).
FIG. 1 is a diagram showing a block configuration of the integrating A/D converter taken out as one column shown in Patent Document 1.
An integrating A/D converter 1 includes a comparator 2, a ripple counter 3 and a transfer bus 4.
In the integrating A/D converter 1, a reference voltage (reference signal) RAMP having a ramp waveform, voltage value of which linearly varies with time is compared to an input voltage VSL in the comparator 2 and the comparison result is outputted as a signal VCO.
Operation of the ripple counter 3 is started or stopped at the timing when the signal VCO varies, and voltage variation is converted into a digital value by counting count periods.